We report a study of the lattice dynamics in superconducting NaFeAs (Tc = 8 K) and doped NaFe0.97Co0.03As (Tc = 20 K) using Raman light scattering. Five of the six phonon modes expected from group theory are observed. In contrast with results obtained on iso-structural and iso-electronic LiFeAs, anomalous broadening of Eg(As) and A1g(Na) modes upon cooling is observed in both samples. In addition, in the Co-doped sample, a superconductivity-induced renormalization of the frequency and linewidth of the B1g(Fe) vibration is observed. This renormalization can not be understood within a single band and simple multi-band approaches. A theoretical model that includes the effects of SDW correlations along with sign-changing s-wave pairing state and interband scattering has been developed to explain the observed behavior of the B1g(Fe) mode.
@article{arxiv.1405.1407,
title = {Superconductivity-induced Phonon Renormalization on NaFe$_{1-x}$Co$_{x}$As},
author = {Y. J. Um and Yunkyu Bang and B. H. Min and Y. S. Kwon and M. Le Tacon},
journal= {arXiv preprint arXiv:1405.1407},
year = {2016}
}